1. Field of the Invention
The present invention relates to an electric brake apparatus for use in braking of a vehicle.
2. Related Art
Electric brake apparatuses, which function to brake a vehicle with use of an electric motor as a driving source, calculate electric current that is contributive only to generation of a thrust force for a linear motion, i.e., thrust force contributive electric current by subtracting, for example, electric current ripples, and electric current corresponding to a resistance against a sliding motion including viscosity of grease at the mechanical portion actuated by the electric motor (viscosity/frictional torque component current) from electric current for driving the electric motor, and then estimate a thrust force by multiplying this thrust force contributive electric current by a function determined from the characteristics of the mechanical portion and the motor, such as an electric current/thrust force conversion function. For example, refer to Japanese Patent Public Disclosure No. 2003-106355. Use of the thus-calculated estimated thrust force eliminates the necessity of a thrust force sensor configured to directly detect a thrust force in some electric brake apparatuses, which thereby can control a brake force without using a sensor.
According to the above-described conventional technique, although the electric brake apparatus can perform control without using any thrust force sensor, the electric brake apparatus may become unable to accurately calculate an estimated thrust force value due to a change in the mechanical portion over time. If this state occurs at left wheel and right wheel sides, this may result in a reduction in the vehicle stability at the time of a brake operation.